docs: def get_stop_times(feed: "Feed", date: Optional[str] = None) -> DataFrame:
      """
      Return a subset of ``feed.stop_times``.
  
      Parameters
      ----------
      feed : Feed
      date : string
          YYYYMMDD date string restricting the output to trips active
          on the date
  
      Returns
      -------
      DataFrame
          Subset of ``feed.stop_times``
  
      Notes
      -----
      Assume the following feed attributes are not ``None``:
  
      - ``feed.stop_times``
      - Those used in :func:`.trips.get_trips`
  
      """
      f = feed.stop_times.copy()
      if date is None:
          return f
  
      g = feed.get_trips(date)
      return f[f["trip_id"].isin(g["trip_id"])]